Do I Need a Rain Gauge If I Have an Irrigation System?
If you have an irrigation system, you may wonder whether you really need a rain gauge. After all, your sprinkler or drip system is already taking care of the watering.
But an irrigation system and a rain gauge do two different jobs. Your irrigation system controls the water you add. A rain gauge tells you how much water nature has already added. Knowing both can help you decide when you actually need to irrigate.
Why Use a Rain Gauge With an Irrigation System?
An irrigation schedule is just that—a schedule. Your plants, lawn and garden don't necessarily need the same amount of supplemental water every week.
If you've had plenty of rain, running your irrigation system on its regular schedule may provide more water than your landscape needs. If you've had very little rain, irrigation may be necessary even if there were a few showers during the week.
A rain gauge gives you an actual rainfall measurement to factor into that decision.
How Much Water Does a Lawn or Garden Need Each Week?
A commonly used rule of thumb is that many established lawns and gardens need around 1 inch of water per week, including both rainfall and irrigation. Actual needs vary with the type of plants, soil, temperature, wind and other conditions, but an inch is a useful starting point.
This is where a rain gauge becomes particularly helpful. If you've measured 0.75 inches of rain during the week, for example, you know that nature has already supplied most of that 1-inch benchmark. Rather than automatically running a full irrigation cycle, you can decide whether your landscape needs additional water.
The goal isn't to hit exactly one inch every week regardless of conditions. It's to know how much rain you've already received before deciding how much more water to add.
Didn't It Rain Enough?
This is one of the harder things to judge without measuring.
A short, heavy shower can look like a lot of rain. Water may be running down the driveway, dripping from the trees and leaving everything looking soaked. But the storm may have been brief and produced less rainfall than you thought.
The opposite can happen with a long, gentle rain. It may not seem particularly dramatic, but it can add up to a significant amount of water over several hours.
A rain gauge takes the guesswork out of how much rain actually fell.
Can a Rain Gauge Help Me Know When to Skip Irrigation?
Yes. That's one of the most useful reasons to have a rain gauge when you already have an irrigation system.
Suppose your landscape has received substantial rainfall over the past few days. Depending on your plants, soil, temperature and other conditions, you may be able to delay your next irrigation cycle rather than adding more water automatically.
On the other hand, if several passing showers have produced only a small amount of measurable rain, your regular watering may still be needed.
What About a Smart Irrigation System or Rain Sensor?
Many modern irrigation systems include rain sensors, soil-moisture sensors or weather-based controllers. These can be very useful, but they aren't quite the same thing as having a rain gauge.
Depending on the system, a smart irrigation controller may use weather data, on-site sensors or a combination of the two to adjust its watering schedule. If it relies on off-site weather data, the rainfall information may not perfectly match what happened at your property. Scattered summer thunderstorms are a good example: one area can get a downpour while another nearby gets very little.
A physical rain gauge gives you a simple way to check what actually happened at your location. If your smart controller thinks you received significant rain but your gauge barely registered any—or vice versa—you have useful information for checking the system's watering decisions.
A rain sensor serves a somewhat different purpose. It's generally designed to interrupt irrigation when conditions are sufficiently wet, rather than to tell you precisely how much rain fell.
Why Not Just Use a Weather App?
Weather apps are useful for forecasts and rainfall information, but rainfall can vary from one location to another. This is especially true with scattered showers and summer thunderstorms.
You may have seen this happen yourself. It's pouring at your house while a friend a few miles away barely gets a drop—or the other way around.
A rain gauge measures the rainfall at your property. For someone trying to decide whether a garden, lawn or landscape needs additional water, that's useful information to have.
Can Measuring Rainfall Help Prevent Overwatering?
Keeping track of rainfall isn't only about saving water. It can also help you avoid giving plants more water than they need.
Consistently wet soil can reduce the amount of oxygen available to roots and can contribute to root problems and some plant diseases. Excess watering can also move nutrients through the soil more quickly than necessary.
That's another reason not to let an irrigation system run automatically without considering recent rainfall. If nature has already done the watering, adding a full irrigation cycle on top of it may not benefit your lawn or garden.
Where Should I Put a Rain Gauge If I Have Sprinklers?
This is important: don't put your rain gauge where your sprinklers can fill it.
If irrigation water is landing in the gauge, you won't know how much of the measurement came from rain and how much came from your sprinkler system.
For measuring rainfall, choose an open location away from sprinkler spray and, as much as possible, away from buildings, trees and other objects that can block or redirect rain.
How Can I Measure How Much Water My Sprinklers Put Out?
You can also measure your irrigation system itself. A common method is known as a catch-can test.
Place several identical straight-sided containers around the area being watered and run the sprinklers for a set amount of time. Then measure the water collected in the containers. This tells you approximately how much water your irrigation system applies during that period and can also reveal areas receiving more or less water than others.
For example, if the containers average 0.25 inches after 15 minutes, your system is applying water at an average rate of about 1 inch per hour. That doesn't necessarily mean you should run it for an hour at once, but now you know your system's approximate application rate and can plan watering accordingly.
Using several containers is important because sprinkler coverage isn't always perfectly even. One part of a lawn may receive considerably more water than another.
Keep your regular rain gauge outside the sprinkler pattern so it can continue doing its regular job: measuring rainfall.
A Rain Gauge and Irrigation System Work Well Together
Having an irrigation system isn't really a reason to skip the rain gauge. In many cases, it's a reason to use one.
Your irrigation system gives you control over how much supplemental water you provide. Your rain gauge helps you keep track of the water that's arriving naturally. And if you take the extra step of measuring your sprinkler output, you can have a much better idea of both sides of the equation.
Used together, that information can help you make watering decisions based on what your lawn and garden have actually received rather than simply what day of the week it is.
And even if your irrigation system does most of the work automatically, it's still interesting to walk outside after a good storm and see exactly how much rain you got.